Ta— and Ta—N-based mixed system coatings for use in Si microelectronics are currently produced by means of plasma-based deposition methods (physical vapour deposition (PVD)). In view of the extreme requirements for ever more highly integrated switching circuits, e.g. uniform coating deposition on textured surfaces, PVD processes are increasingly being pushed to the limits of what is technically feasible. For these applications, chemical gas phase deposition methods (chemical vapour deposition (CVD)) through to film deposition with atomic layer precision using a special CVD method known as atomic layer deposition (ALD) are increasingly coming into use. For these CVD processes the appropriate chemical starting materials for the individual elements must naturally be available for the coatings that are required in each case.
At present, halides such as e.g. TaCl5, TaBr5, see WO 2000065123 A1, A. E. Kaloyeros et al., J. Electrochem. Soc. 146 (1999), p. 170-176, or K. Hieber, Thin Solid Films 24 (1974), p. 157-164), are mainly used for the CVD of Ta-based coating structures. There are a number of disadvantages associated with this practice. Firstly, halogen radicals are undesirable in many ways for the formation of complex coating structures because of their caustic/corrosive properties, and secondly tantalum halides exhibit disadvantages due to their low volatility and difficult processing characteristics as high-melting solids. Simple tantalum(V) amides, such as e.g. ((CH3)2N)5Ta, are likewise proposed, see e.g. Fix et al., Chem. Mater., 5 (1993), p. 614-619. However, with the simple amides only certain decomposition ratios of Ta to N can usually be established, which make the accurate control of the individual concentrations of elements in the coatings more difficult. In many cases Ta(V) nitride films are formed (see e.g. Fix et al.: Ta3N5) rather than the desired electrically conductive Ta(III) nitride coatings (TaN). Furthermore, the films produced with these starting materials very often exhibit high, undesirable concentrations of carbon. For that reason Tsai et al., Appl. Phys. Lett. 67(8), (1995), p. 1128-1130, proposed t-BuN═Ta(NEt2)3 in TaN CVD at 600° C. Because of its relatively low volatility, this compound requires a high plant temperature and is therefore not very compatible with the typical production processes for integrated switching circuits. Other, similar tantalum amide imides have also been proposed, see e.g. Chiu et al., J. Mat. Sci. Lett. 11 (1992), p. 96-98, with which, however, without additional reactive gas, high carbon contents were obtained in the tantalum nitride coatings. More recently, other tantalum nitride precursors have been proposed, e.g. by Bleau et al., Polyhedron 24(3), (2005), p. 463-468, which because of their complexity and laborious production exhibit disadvantages from the outset, or special cyclopentadienyl compounds, which either inevitably lead to TaSiN (not tantalum nitride) or require an additional, not otherwise specified nitrogen source (Kamepalli et al., US Pat. Appl. Publ. 2004142555 A1, Priority Jan. 16, 2003, ATMI, Inc.). In U.S. Pat. No. 6,593,484 (Kojundo Chemicals Laboratory Co., Ltd., Japan) a suitable special tantalum amide imide is proposed, although the specified synthesis can only be reproduced poorly and with difficulty.
A considerable need can thus be identified for other, novel precursors for TaN coatings which do not have the aforementioned disadvantages or which at least bring about clear improvements.